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The Carbon Trust has invested in the design of innovative transfer vessels through the Offshore Wind Accelerator, with the aim to be able to transfer the crew in up to 3m significant wave height (Hs) sea states.

Hs, a statistical measure of wave height, is one of the determining factors which affects that most important of factors for bow transfer - the bow displacement and acceleration, although other sea characteristics also do: the current speed and direction, wind speed and direction, wave period and direction also affect when and where the bow moves, so to target the critical requirement to allow the technicians to transfer comes from adapting the vessel design to be less responsive to the environmental conditions expected on location.

Increasing bow friction to increase the force between the fender and the boat landing reduces motion. To increase the friction force, more power from the propellers or jets creates more pressure on the bow, with a limit on the amount of force acceptable in the design of the boat landing itself and the structural strength of the vessel in accommodating the force on the bow.

CONSIDERATIONS There are however downsides, increased friction means the increasing deterioration of surface paints and coatings on the landings, which returns an increased cost and offshore activity of repainting the boat landings.

Also, from an operational perspective, the sudden overcoming of the friction force can disrupt the technician’s judgement and prediction of a suitable time to step across. Intelligent fender systems, such as developed by RG Seasight Fender and Strainstall’s Intelligent Fender System (IFS) sense the force on the bow to give a measurement and visual display to the skipper of the force being applied.

ACTIVE FENDERING SYSTEMS Active fendering systems, such as those designed by BMT Nigel Gee and built into a number of vessels most recently the Njord Magni, are able to reduce the impact forces imposed on the boat landing from the vessel contact. In this case, the middle section of the bow contains an impact damping system which reduces impact loads on contact with the boat landing. A proportion of the impact energy is absorbed by the conventional fender and the remainder is absorbed by the active fender.


Ultimately there is also the need to reduce the number of visits and to make optimum use of the time on the turbine. Innovation in remote monitoring and inspection reduces the need to transfer personnel for physical inspection. Risk based O&M predictions are based on an understanding of damage or wear regimes according to the loading and environmental conditions.

The long term aim being to achieve site- specific inspection and maintenance regime for each asset, rather than a scheduled periodic inspection. Lloyd’s Register is working to apply Risk Based Inspection through the RBMI software to help achieve this.


These techniques rely on condition monitoring and information transfer through the SCADA system, which is well-established, but one can envisage a world of pervasive sensing with embedded sensors such as Metal Embedded Optical Fibre Sensors and long range ultrasonic (LRU) with acoustic emission technique in combination helping improve real-time asset monitoring on a more distributed and asset-wide perspective. A number of joint- industry projects are ongoing in this space.

TWi as part of the Technology Strategy Board funded CM-drive have developed non-contact microphone arrays for structural health monitoring of rotating machinery in the onshore environment.

With sensors located in the nacelle of the structure, acoustic signatures are detected from healthy and worn drivetrains to indicate their relative condition. The combined condition monitoring capabilities including Motor Current Signature Analysis,

Operational Modal Analysis and Acoustic Emission are applied under the CMSWind project funded by the EU under FP7.

Sensors are used to detect the condition of the generator, gearbox bearings and main shaft with the aim of detecting the slip-ring corrosion and shaft/bearing misalignment and wireless sensor technology aims to allow the inclusion of sensors across rotating interfaces.


The feasibility of in-service monitoring of the structural health of blades using Acoustic Emission is also being investigated. An experiment, developed at the National Renewable Energy Centre Blade Test Facility, tested a 46 metre long blade in which de-bonding had been initiated.

The blade was tested under fatigue loads using Compact Resonant Masses (CRMs) to excite the blade, accurately simulating in-service load conditions over a 6 week period. During the tests AE monitoring was performed with a sensor network to confirm that it is possible to extract and classify AE events. All promising techniques to help active improved remote monitoring.


Back to the bow of the CTV and the step across to the turbine ladder; innovations in CTV design and contracting are helping the industry move towards increasing accessibility and expanding weather windows in the short term.

But with the prospect of improved analytics of unstructured data derived from remote sensor systems, we also look to a future when remote diagnosis will optimise the use of offshore transfers and specialist support will be remotely provided to technicians to reduce O&M costs.

Lloyds Register


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